1. Technical Field
The present disclosure relates to acoustic devices and method for generating sound waves, particularly, to a carbon nanotube based thermoacoustic device and method for generating sound waves using the thermoacoustic effect.
2. Description of Related Art
Acoustic devices generally include a signal device and a sound wave generator. The signal device inputs signals to the sound wave generator such as a loudspeaker. Loudspeaker is an electro-acoustic transducer that converts electrical signals into sound.
There are different types of loudspeakers that can be categorized according by their working principles, such as electro-dynamic loudspeakers, electromagnetic loudspeakers, electrostatic loudspeakers and piezoelectric loudspeakers. However, the various types ultimately use mechanical vibration to produce sound waves, in other words they all achieve “electro-mechanical-acoustic” conversion. Among the various types, the electro-dynamic loudspeakers are most widely used.
Referring to FIG. 21, the electro-dynamic loudspeaker 100, according to the prior art, typically includes a voice coil 102, a magnet 104 and a cone 106. The voice coil 102 is an electrical conductor, and is placed in the magnetic field of the magnet 104. By applying an electrical current to the voice coil 102, a mechanical vibration of the cone 106 is produced due to the interaction between the electromagnetic field produced by the voice coil 102 and the magnetic field of the magnets 104, thus producing sound waves by kinetically pushing the air. However, the structure of the electric-powered loudspeaker 100 is dependent on magnetic fields and often weighty magnets.
Thermoacoustic effect is a conversion between heat and acoustic signals. The thermoacoustic effect is distinct from the mechanism of the conventional loudspeaker, which the pressure waves are created by the mechanical movement of the diaphragm. When signals are inputted into a thermoacoustic element, heating is produced in the thermoacoustic element according to the variations of the signal and/or signal strength. Heat is propagated into surrounding medium. The heating of the medium causes thermal expansion and produces pressure waves in the surrounding medium, resulting in sound wave generation. Such an acoustic effect induced by temperature waves is commonly called “the thermoacoustic effect”.
A thermophone based on the thermoacoustic effect was created by H. D. Arnold and I. B. Crandall (H. D. Arnold and I. B. Crandall, “The thermophone as a precision source of sound”, Phys. Rev. 10, pp 22-38 (1917)). They used platinum strip with a thickness of 7×10−5 cm as a thermoacoustic element. The heat capacity per unit area of the platinum strip with the thickness of 7×10−5 cm is 2×10−4 J/cm2·K. However, the thermophone adopting the platinum strip, listened to the open air, sounds extremely weak because the heat capacity per unit area of the platinum strip is too high.
What is needed, therefore, is to provide an effective thermoacoustic device having a simple lightweight structure that is not dependent on magnetic fields, able to produce sound without the use of vibration, and able to move and flex without an effect on the sound waves produced.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one exemplary embodiment of the present thermoacoustic device and method for generating sound waves, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.